/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.xml;

import java.io.IOException;
import java.io.InputStream;

import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.xml.sax.EntityResolver;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.parsing.EmptyReaderEventListener;
import org.springframework.beans.factory.parsing.FailFastProblemReporter;
import org.springframework.beans.factory.parsing.NullSourceExtractor;
import org.springframework.beans.factory.parsing.ProblemReporter;
import org.springframework.beans.factory.parsing.ReaderEventListener;
import org.springframework.beans.factory.parsing.SourceExtractor;
import org.springframework.beans.factory.support.AbstractBeanDefinitionReader;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.core.Constants;
import org.springframework.core.io.DescriptiveResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.EncodedResource;
import org.springframework.util.Assert;
import org.springframework.util.xml.SimpleSaxErrorHandler;
import org.springframework.util.xml.XmlValidationModeDetector;

/**
 * XML格式的bean定义的读取器。代理{@link BeanDefinitionDocumentReader}的真正实现类。<br/>
 * Bean definition reader for XML bean definitions. Delegates the actual XML
 * document reading to an implementation of the
 * {@link BeanDefinitionDocumentReader} interface.
 * 
 * <p>
 * Typically applied to a
 * {@link org.springframework.beans.factory.support.DefaultListableBeanFactory}
 * or a {@link org.springframework.context.support.GenericApplicationContext}.
 * 
 * <p>
 * This class loads a DOM document and applies the BeanDefinitionDocumentReader
 * to it. The document reader will register each bean definition with the given
 * bean factory, talking to the latter's implementation of the
 * {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}
 * interface.
 * 
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 26.11.2003
 * @see #setDocumentReaderClass
 * @see BeanDefinitionDocumentReader
 * @see DefaultBeanDefinitionDocumentReader
 * @see BeanDefinitionRegistry
 * @see org.springframework.beans.factory.support.DefaultListableBeanFactory
 * @see org.springframework.context.support.GenericApplicationContext
 */
public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

	/**
	 * Indicates that the validation should be disabled.
	 */
	public static final int VALIDATION_NONE = 0;

	/**
	 * Indicates that the validation mode should be detected automatically.
	 */
	public static final int VALIDATION_AUTO = XmlValidationModeDetector.VALIDATION_AUTO;

	/**
	 * Indicates that DTD validation should be used.
	 */
	public static final int VALIDATION_DTD = XmlValidationModeDetector.VALIDATION_DTD;

	/**
	 * Indicates that XSD validation should be used.
	 */
	public static final int VALIDATION_XSD = XmlValidationModeDetector.VALIDATION_XSD;

	/** Constants instance for this class */
	private static final Constants constants = new Constants(
			XmlBeanDefinitionReader.class);

	private boolean namespaceAware;

	private int validationMode = VALIDATION_AUTO;

	private Class parserClass;

	private Class documentReaderClass = DefaultBeanDefinitionDocumentReader.class;

	private ProblemReporter problemReporter = new FailFastProblemReporter();

	private ReaderEventListener eventListener = new EmptyReaderEventListener();

	private SourceExtractor sourceExtractor = new NullSourceExtractor();

	private NamespaceHandlerResolver namespaceHandlerResolver;

	private DocumentLoader documentLoader = new DefaultDocumentLoader();

	private EntityResolver entityResolver;

	private ErrorHandler errorHandler = new SimpleSaxErrorHandler(logger);

	private final XmlValidationModeDetector validationModeDetector = new XmlValidationModeDetector();

	/**
	 * Create new XmlBeanDefinitionReader for the given bean factory.
	 * 
	 * @param beanFactory
	 *            the BeanFactory to load bean definitions into, in the form of
	 *            a BeanDefinitionRegistry
	 */
	public XmlBeanDefinitionReader(BeanDefinitionRegistry beanFactory) {
		super(beanFactory);
	}

	/**
	 * Set whether or not the XML parser should be XML namespace aware. Default
	 * is "false".
	 */
	public void setNamespaceAware(boolean namespaceAware) {
		this.namespaceAware = namespaceAware;
	}

	/**
	 * Set if the XML parser should validate the document and thus enforce a
	 * DTD.
	 * 
	 * @deprecated as of Spring 2.0: superseded by "validationMode"
	 * @see #setValidationMode
	 */
	public void setValidating(boolean validating) {
		this.validationMode = (validating ? VALIDATION_AUTO : VALIDATION_NONE);
	}

	/**
	 * Set the validation mode to use by name. Defaults to
	 * {@link #VALIDATION_AUTO}.
	 */
	public void setValidationModeName(String validationModeName) {
		setValidationMode(constants.asNumber(validationModeName).intValue());
	}

	/**
	 * Set the validation mode to use. Defaults to {@link #VALIDATION_AUTO}.
	 */
	public void setValidationMode(int validationMode) {
		this.validationMode = validationMode;
	}

	/**
	 * Specify which
	 * {@link org.springframework.beans.factory.parsing.ProblemReporter} to use.
	 * Default implementation is
	 * {@link org.springframework.beans.factory.parsing.FailFastProblemReporter}
	 * which exhibits fail fast behaviour. External tools can provide an
	 * alternative implementation that collates errors and warnings for display
	 * in the tool UI.
	 */
	public void setProblemReporter(ProblemReporter problemReporter) {
		this.problemReporter = (problemReporter != null ? problemReporter
				: new FailFastProblemReporter());
	}

	/**
	 * Specify which {@link ReaderEventListener} to use. Default implementation
	 * is EmptyReaderEventListener which discards every event notification.
	 * External tools can provide an alternative implementation to monitor the
	 * components being registered in the BeanFactory.
	 */
	public void setEventListener(ReaderEventListener eventListener) {
		this.eventListener = (eventListener != null ? eventListener
				: new EmptyReaderEventListener());
	}

	/**
	 * Specify the {@link SourceExtractor} to use. The default implementation is
	 * {@link NullSourceExtractor} which simply returns <code>null</code> as the
	 * source object. This means that during normal runtime execution no
	 * additional source metadata is attached to the bean configuration
	 * metadata.
	 */
	public void setSourceExtractor(SourceExtractor sourceExtractor) {
		this.sourceExtractor = (sourceExtractor != null ? sourceExtractor
				: new NullSourceExtractor());
	}

	/**
	 * Specify the {@link NamespaceHandlerResolver} to use. If none is specified
	 * a default instance will be created by
	 * {@link #createDefaultNamespaceHandlerResolver()}.
	 */
	public void setNamespaceHandlerResolver(
			NamespaceHandlerResolver namespaceHandlerResolver) {
		this.namespaceHandlerResolver = namespaceHandlerResolver;
	}

	/**
	 * Specify the {@link DocumentLoader} to use. The default implementation is
	 * {@link DefaultDocumentLoader} which loads {@link Document} instances
	 * using JAXP.
	 */
	public void setDocumentLoader(DocumentLoader documentLoader) {
		this.documentLoader = (documentLoader != null ? documentLoader
				: new DefaultDocumentLoader());
	}

	/**
	 * Set a SAX entity resolver to be used for parsing. By default,
	 * BeansDtdResolver will be used. Can be overridden for custom entity
	 * resolution, for example relative to some specific base path.
	 * 
	 * @see BeansDtdResolver
	 */
	public void setEntityResolver(EntityResolver entityResolver) {
		this.entityResolver = entityResolver;
	}

	/**
	 * Return the EntityResolver to use, building a default resolver if none
	 * specified.
	 */
	protected EntityResolver getEntityResolver() {
		if (this.entityResolver == null) {
			// Determine default EntityResolver to use.
			ResourceLoader resourceLoader = getResourceLoader();
			if (resourceLoader != null) {
				this.entityResolver = new ResourceEntityResolver(resourceLoader);
			} else {
				this.entityResolver = new DelegatingEntityResolver(getBeanClassLoader());
			}
		}
		return this.entityResolver;
	}

	/**
	 * Set an implementation of the <code>org.xml.sax.ErrorHandler</code>
	 * interface for custom handling of XML parsing errors and warnings.
	 * <p>
	 * If not set, a default SimpleSaxErrorHandler is used that simply logs
	 * warnings using the logger instance of the view class, and rethrows errors
	 * to discontinue the XML transformation.
	 * 
	 * @see SimpleSaxErrorHandler
	 */
	public void setErrorHandler(ErrorHandler errorHandler) {
		this.errorHandler = errorHandler;
	}

	/**
	 * Set the XmlBeanDefinitionParser implementation to use, responsible for
	 * the actual parsing of XML bean definitions.
	 * 
	 * @deprecated as of Spring 2.0: superseded by "documentReaderClass"
	 * @see #setDocumentReaderClass
	 * @see XmlBeanDefinitionParser
	 */
	public void setParserClass(Class parserClass) {
		if (this.parserClass == null
				|| !XmlBeanDefinitionParser.class.isAssignableFrom(parserClass)) {
			throw new IllegalArgumentException(
					"'parserClass' must be an XmlBeanDefinitionParser");
		}
		this.parserClass = parserClass;
	}

	/**
	 * Specify the BeanDefinitionDocumentReader implementation to use,
	 * responsible for the actual reading of the XML bean definition document.
	 * <p>
	 * Default is DefaultBeanDefinitionDocumentReader.
	 * 
	 * @param documentReaderClass
	 *            the desired BeanDefinitionDocumentReader implementation class
	 * @see BeanDefinitionDocumentReader
	 * @see DefaultBeanDefinitionDocumentReader
	 */
	public void setDocumentReaderClass(Class documentReaderClass) {
		if (documentReaderClass == null
				|| !BeanDefinitionDocumentReader.class
						.isAssignableFrom(documentReaderClass)) {
			throw new IllegalArgumentException(
					"documentReaderClass must be an implementation of the BeanDefinitionDocumentReader interface");
		}
		this.documentReaderClass = documentReaderClass;
	}

	/**
	 * 根据指定的XML文件，加载bean定义。<br>
	 * Load bean definitions from the specified XML file.
	 * 
	 * @param resource
	 *            the resource descriptor for the XML file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException
	 *             in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
		return loadBeanDefinitions(new EncodedResource(resource));
	}

	/**
	 * 从指定的XML文件，加载bean定义。<br/>
	 * Load bean definitions from the specified XML file.
	 * 
	 * @param encodedResource
	 *            the resource descriptor for the XML file, allowing to specify
	 *            an encoding to use for parsing the file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException
	 *             in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(EncodedResource encodedResource)
			throws BeanDefinitionStoreException {
		Assert.notNull(encodedResource, "EncodedResource must not be null");
		if (logger.isInfoEnabled()) {
			logger.info("Loading XML bean definitions from "
					+ encodedResource.getResource());
		}

		try {
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
			} finally {
				inputStream.close();
			}
		} catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"IOException parsing XML document from "
							+ encodedResource.getResource(), ex);
		}
	}

	/**
	 * Load bean definitions from the specified XML file.
	 * 
	 * @param inputSource
	 *            the SAX InputSource to read from
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException
	 *             in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(InputSource inputSource)
			throws BeanDefinitionStoreException {
		return loadBeanDefinitions(inputSource, "resource loaded through SAX InputSource");
	}

	/**
	 * Load bean definitions from the specified XML file.
	 * 
	 * @param inputSource
	 *            the SAX InputSource to read from
	 * @param resourceDescription
	 *            a description of the resource (can be <code>null</code> or
	 *            empty)
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException
	 *             in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(InputSource inputSource, String resourceDescription)
			throws BeanDefinitionStoreException {

		return doLoadBeanDefinitions(inputSource, new DescriptiveResource(
				resourceDescription));
	}

	/**
	 * 从指定的XML中，真正加载bean定义。<br/>
	 * Actually load bean definitions from the specified XML file.
	 * 
	 * @param inputSource
	 *            the SAX InputSource to read from
	 * @param resource
	 *            the resource descriptor for the XML file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException
	 *             in case of loading or parsing errors
	 */
	protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			int validationMode = getValidationModeForResource(resource);
			Document doc = this.documentLoader.loadDocument(inputSource,
					getEntityResolver(), this.errorHandler, validationMode,
					this.namespaceAware);
			return registerBeanDefinitions(doc, resource);
		} catch (BeanDefinitionStoreException ex) {
			throw ex;
		} catch (SAXParseException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line "
					+ ex.getLineNumber() + " in XML document from " + resource
					+ " is invalid", ex);
		} catch (SAXException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"XML document from " + resource + " is invalid", ex);
		} catch (ParserConfigurationException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Parser configuration exception parsing XML from " + resource, ex);
		} catch (IOException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"IOException parsing XML document from " + resource, ex);
		} catch (Throwable ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Unexpected exception parsing XML document from " + resource, ex);
		}
	}

	/**
	 * Gets the validation mode for the specified {@link Resource}. If no
	 * explicit validation mode has been configured then the validation mode is
	 * {@link #detectValidationMode detected}.
	 */
	private int getValidationModeForResource(Resource resource) {
		if (this.validationMode != VALIDATION_AUTO) {
			return this.validationMode;
		}
		int detectedMode = detectValidationMode(resource);
		if (detectedMode != VALIDATION_AUTO) {
			return detectedMode;
		}
		// Hmm, we didn't get a clear indication... Let's assume XSD,
		// since apparently no DTD declaration has been found up until
		// detection stopped (before finding the document's root tag).
		return VALIDATION_XSD;
	}

	/**
	 * Detects which kind of validation to perform on the XML file identified by
	 * the supplied {@link Resource}. If the file has a <code>DOCTYPE</code>
	 * definition then DTD validation is used otherwise XSD validation is
	 * assumed.
	 */
	protected int detectValidationMode(Resource resource) {
		if (resource.isOpen()) {
			throw new BeanDefinitionStoreException(
					"Passed-in Resource ["
							+ resource
							+ "] contains an open stream: "
							+ "cannot determine validation mode automatically. Either pass in a Resource "
							+ "that is able to create fresh streams, or explicitly specify the validationMode "
							+ "on your XmlBeanDefinitionReader instance.");
		}

		InputStream inputStream;
		try {
			inputStream = resource.getInputStream();
		} catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"Unable to determine validation mode for ["
							+ resource
							+ "]: cannot open InputStream. "
							+ "Did you attempt to load directly from a SAX InputSource without specifying the "
							+ "validationMode on your XmlBeanDefinitionReader instance?",
					ex);
		}

		try {
			return this.validationModeDetector.detectValidationMode(inputStream);
		} catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"Unable to determine validation mode for [" + resource
							+ "]: an error occurred whilst reading from the InputStream.",
					ex);
		}
	}

	/**
	 * Register the bean definitions contained in the given DOM document. Called
	 * by <code>loadBeanDefinitions</code>.
	 * <p>
	 * Creates a new instance of the parser class and invokes
	 * <code>registerBeanDefinitions</code> on it.
	 * 
	 * @param doc
	 *            the DOM document
	 * @param resource
	 *            the resource descriptor (for context information)
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException
	 *             in case of parsing errors
	 * @see #loadBeanDefinitions
	 * @see #setDocumentReaderClass
	 * @see BeanDefinitionDocumentReader#registerBeanDefinitions
	 */
	public int registerBeanDefinitions(Document doc, Resource resource)
			throws BeanDefinitionStoreException {
		// Support old XmlBeanDefinitionParser SPI for backwards-compatibility.
		if (this.parserClass != null) {
			XmlBeanDefinitionParser parser = (XmlBeanDefinitionParser) BeanUtils
					.instantiateClass(this.parserClass);
			return parser.registerBeanDefinitions(this, doc, resource);
		}
		// Read document based on new BeanDefinitionDocumentReader SPI.
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		int countBefore = getBeanFactory().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getBeanFactory().getBeanDefinitionCount() - countBefore;
	}

	/**
	 * Create the {@link BeanDefinitionDocumentReader} to use for actually
	 * reading bean definitions from an XML document.
	 * <p>
	 * Default implementation instantiates the specified "documentReaderClass".
	 * 
	 * @see #setDocumentReaderClass
	 */
	protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
		return (BeanDefinitionDocumentReader) BeanUtils
				.instantiateClass(this.documentReaderClass);
	}

	/**
	 * Create the {@link XmlReaderContext} to pass over to the document reader.
	 */
	protected XmlReaderContext createReaderContext(Resource resource) {
		if (this.namespaceHandlerResolver == null) {
			this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
		}
		return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
				this.sourceExtractor, this, this.namespaceHandlerResolver);
	}

	/**
	 * Create the default implementation of {@link NamespaceHandlerResolver}
	 * used if none is specified. Default implementation returns an instance of
	 * {@link DefaultNamespaceHandlerResolver}.
	 */
	protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
		return new DefaultNamespaceHandlerResolver(getResourceLoader().getClassLoader());
	}

}
